Enrico Berti and others hold that Aquinas’s notion of God as ipsum esse subsistens conflicts with Aristotle’s view that positing an Idea of being treats being as a genus and nullifies all differences. The paper first shows how one of Aquinas’s ways of distinguishing esse from essence supposes an intimate tie between a thing’s esse and its differentia. Then it argues that for Aquinas the (one) divine essence differs from the (manifold) “essence of esse.” God is his very esse. This somehow “contains” all esse, but it also transcends it, because although simple, it also “contains” all forms and differentiae.